The first and preliminary results of the photometry of Large Yield Radiometer (LYRA) and Sun Watcher using Active Pixel system detector and Image Processing (SWAP) onboard PROBA2 are presented in this paper. To study the day-to-day variations of LYRA irradiance, we have compared the LYRA irradiance values (observed Sun as a star) measured in Aluminum filter channel (171？？–500？？) with spatially resolved full-disk integrated intensity values measured with SWAP (174？？) and Ca II K 1 ？ index values (ground-based observations from NSO/Sac Peak) for the period from 01 April 2010 to 15 Mar 2011. We found that there is a good correlation between these parameters. This indicates that the spatial resolution of SWAP complements the high temporal resolution of LYRA. Hence SWAP can be considered as an additional radiometric channel. Also the K emission index is the integrated intensity (or flux) over a 1 ？ band centered on the K line and is proportional to the total emission from the chromosphere; this comparison clearly explains that the LYRA irradiance variations are due to the various magnetic features, which are contributing significantly. In addition to this we have made an attempt to segregate coronal features from full-disk SWAP images. This will help to understand and determine the actual contribution of the individual coronal feature to LYRA irradiance variations. 1. Introduction The Sun is the primary source of energy responsible for governing both the weather and climate of Earth. For that reason alone one would expect that changes in the amount and type of energy Earth received from the Sun could alter weather and climate on the Earth. Hence the knowledge of the solar spectral irradiance is of large interest to solar physics, aeronomy, and to other fields of heliospheric or planetary research. The solar ultraviolet (UV) irradiance below 3000？？ is the main source of the energy converted in the Earth’s atmosphere, controlling its thermal structure, dynamics, and chemistry through photodissociation and photoionization [1]. Because of these, changes in UV irradiance influence the concentration of the ozone in the Earth’s atmosphere [2, 3] and may play a significant role in the process of the global warming. The balance of the ozone formed by radiation below 2400？？ in the stratosphere and mesosphere is of special interest for life and mankind. However, the photons above 2000？？ get dissociated in the stratosphere and disturb the balance of the ozone (e.g., [4, 5]). This is because the ozone gas is produced naturally in the stratosphere where it strongly
References
[1]
G. J. Rottman, “Observations of solar UV and EUV variability,” Advances in Space Research, vol. 8, no. 7, pp. 53–66, 1988.
[2]
G. Brasseur, “The response of the middle atmosphere to long-term and short-term solar variability: a two-dimensional model,” Journal of Geophysical Research, vol. 982, pp. 23079–23090, 1993.
[3]
L. L. Hood, J. L. Jirikowic, and J. P. McCormack, “Quasi-decadal variability of the stratosphere: in uence of long-term solar ultraviolet variations,” Journal of Atmospheric Sciences, vol. 50, pp. 3941–3958, 1993.
[4]
T. Egorova, E. Rozanov, E. Manzini et al., “Chemical and dynamical response to the 11-year variability of the solar irradiance simulated with a chemistry-climate model,” Geophysical Research Letters, vol. 31, no. 6, Article ID L06119, 2004.
[5]
E. Rozanov, M. Schraner, M. Wild, et al., “Assessment of the Ozone and Temperature Trends for 1975–2000 with a transient Chemistry-Climate Model,” in Proceedings of the 35th COSPAR Scientific Assembly, J.-P. Paillé, Ed., vol. 35, p. 2640, 2004.
[6]
H. Hudson and R. Willson, “The nature of the solar-cycle variation of total irradiance,” in Solar Radiative Output Variations, P. Foukal, Ed., p. 318, 1988.
[7]
C. Frohlich, “Irradiance observations of the sun,” in Poster Proceedings from IAU Colloquium 143: The Sun as a Variable Star: Solar and Stellar Irradiance Variations, J. M. Pap, C. Frohlich, H. S. Hudson, and S. K. Solanki, Eds., p. 28, 1994.
[8]
P. Foukal and J. Lean, “Magnetic modulation of solar luminosity by photospheric activity,” Astrophysical Journal, vol. 328, pp. 347–357, 1988.
[9]
R. Kariyappa and J. M. Pap, “Contribution of chromospheric features to uv irradiance variability from spatially-resolved ca ii k spectroheliograms i. A New Method of Analysis and Preliminary Results,” Solar Physics, vol. 167, no. 1-2, pp. 115–123, 1996.
[10]
J. R. Worden, O. R. White, and T. N. Woods, “Evolution of chromospheric structures derived from Ca II K spectroheliograms: implications for solar ultraviolet irradiance variability,” Astrophysical Journal, vol. 496, no. 2, pp. 998–1014, 1998.
[11]
J. Lean, “Solar ultraviolet irradiance variations—a review,” Journal of Geophysical Research, vol. 92, pp. 839–868, 1987.
[12]
H. P. Warren, J. T. Mariska, and J. Lean, “A new model of solar EUV irradiance variability 1. Model formulation,” Journal of Geophysical Research A, vol. 106, no. 8, pp. 15745–15757, 2001.
[13]
T. Woods, F. Eparvier, and D. Woodraska, “Solar ultraviolet variability during the TIMED mission,” in Proceedings of the AGU Fall Meeting Abstracts, p. B2, San Francisco, Calif, USA, December 2003.
[14]
J. L. Lean, H. P. Warren, J. T. Mariska, and J. Bishop, “A new model of solar EUV irradiance variability 2. Comparisons with empirical models and observations and implications for space weather,” Journal of Geophysical Research A, vol. 108, no. 2, article no. 1059, 2003.
[15]
J. F. Hochedez, W. Schmutz, Y. Stockman et al., “LYRA, a solar UV radiometer on Proba2,” Advances in Space Research, vol. 37, no. 2, pp. 303–312, 2006.
[16]
A. Benmoussa, I. E. Dammasch, J.-F. Hochedez, et al., “Preight calibration of LYRA, the solar VUV radiometer on board PROBA2,” Astronomy and Astrophysics, vol. 508, pp. 1085–1094, 2009.
[17]
D. Berghmans, J. F. Hochedez, J. M. Defise, et al., “SWAP onboard PROBA 2, a new EUV imager for solar monitoring,” Advances in Space Research, vol. 38, pp. 1807–1811, 2006.
[18]
J.-P. Halain, D. Berghmans, J.-M. Defise, et al., “First light of SWAP on-board PROBA2,” in Space Telescopes and Instrumentation 2010: Ultraviolet to Gamma Ray, vol. 7732 of Society of Photo-Optical Instrumentation Engineers (SPIE) Conference Series, July 2010.
[19]
O. C. Wilson, “Flux measurements at the centers of stellar h- and kLines,” Astrophysical Journal, vol. 153, p. 221, 1968.
[20]
R. Kariyappa and K. R. Sivaraman, “Variability of the solar chromospheric network over the solar cycle,” Solar Physics, vol. 152, no. 1, pp. 139–144, 1994.
[21]
R. Kariyappa, J. M. Pap, K. S. Balasubramaniam, and J. R. Kuhn, “Preliminary results of the analysis of CAII K spectroheliograms,” in Helioseismology, vol. 376 of ESA Special Publication, p. 429, 1995.
[22]
R. Kariyappa, “Quiet-sun variability with the solar cycle,” in High Resolution Solar Physics: Theory, Observations, and Techniques, T. R. Rimmele, K. S. Balasubramaniam, and R. R. Radick, Eds., vol. 183 of Astronomical Society of the Pacific Conference Series, p. 501, 1999.
[23]
R. Kariyappa, “Call K imaging to understand UV irradiance variability,” Journal of Astrophysics and Astronomy, vol. 21, no. 3-4, pp. 293–297, 2000.
[24]
R. Kariyappa and K. R. Sivaraman, “Variability of caII K emission flux over the solar cycle,” Bulletin of the Astronomical Society of India, vol. 33, pp. 365–365, 2005.
[25]
R. Kariyappa and L. Dame, “Contribution of chromospheric features to UV irradiance variability,” in Proceedings of the IAU Joint Discussion, vol. 8, August 2006.
[26]
M. K. V. Bappu and K. R. Sivaraman, “K emission-line widths and the solar chromosphere,” Solar Physics, vol. 17, no. 2, pp. 316–330, 1971.
